first off, yes....he's relatively unhurt, but i seriously doubt he was seen walking around. i talked to him last night, and he's doing ok. that's all i'm willing to say about that, but your concern is appreciated i'm sure.
second....all the safety gear worked, but he hit HARD. multiple miata guys told me that it's the biggest impact they've seen one of these cars take. some stress cracks in the cage, and a slightly bent rear downtube, but it all did it's job.
third....it's really hard to say what happened, and i don't really want to speculate about it as the car is so comprehensively destroyed there's no way anything can be said for certain.
in the end all that matters is that it looks like he'll be fine with no long-term effects.